1. Field of the Invention
The present invention relates to an ignition system for internal combustion engines.
2. Description of the Related Art
A conventional ignition system for internal combustion engines is disclosed in U.S. Pat. No. 4,440,130. This ignition system includes a timing signal detector for generating a pulse signal having a pulse spacing corresponding to the rotation speed of the engine, voltage storing means for storing a voltage corresponding to the rotation speed of the engine, and sawtooth wave generating means for generating a sawtooth wave having a period corresponding to that of the pulse signal and having a slope corresponding to the stored voltage in the voltage storing means. This ignition system compares the voltage level of the sawtooth wave generated from the sawtooth wave generating means with a reference voltage for every period of pulse signals generated from the timing signal generator, so that when there is a deviation or difference between the two voltages, the voltage level of the stored voltage stored in the voltage storing means is varied according to the difference and the slope of the sawtooth wave is varied thus rapidly producing an accurate stored voltage corresponding to the rotation speed and thereby accurately performing a duty cycle control for controlling the dwell time of the ignition coil.
However, since this conventional ignition system corrects the stored voltage in the voltage storing means thus controlling the next dwell time of the ignition coil, when the rotation speed of the engine increases rapidly, the then current dwell time of the ignition coil must be maintained for a given period of time. Also, since the slope of the sawtooth wave voltage is varied when the stored voltage is varied and since the sawtooth wave voltage is discharged within the duration time of the pulse signal, the minimum value of the ignition coil dwell time becomes the duration time of the pulse signal. On account of these reasons, the conventional ignition system is disadvantageous in that during the steady-state operation of the engine the dwell time of the ignition coil must be increased thus increasing the heat generation of the ignition coil. Another disadvantage is that while the pulse width of the pulse signal must preliminarily be decreased so as to reduce the heat generation of the ignition coil, if the pulse width is decreased to an extent that any excessive heat generation of the ignition coil is prevented, when rapidly increasing the rotation speed of the engine, the then current dwell time of the ignition coil becomes insufficient thus causing the engine to misfire.